It is known to form an optical device by enclosing a constant volume of fluid between a deformable membrane and a support having a face extending substantially parallel to the membrane.
A peripheral anchoring area of the membrane is connected to the support.
The central part constitutes the optical field of the device.
An actuation device of the membrane is arranged in an area of the membrane, said actuation area located between the peripheral anchoring area and the central part.
Said actuation device comprises one or more actuators capable of bending towards the fluid and/or in the direction opposite the fluid under application of electrical actuation voltage.
Bending of the actuation device causes a variation in the thickness of fluid between the membrane and the face of the support opposite the membrane, which guides the flow of the volume of fluid located in this region either towards the centre of the device or towards the periphery of the device. “Flow region” refers that part of the volume of fluid located between the actuation area of the membrane and the face of the support opposite the membrane.
The effect of the flow of the volume of fluid is to modify the fluid pressure to which the central part of the membrane is subjected, manifest by deformation of said central part and modifying the focal length of the device.
The response time of such an optical device is defined as being the interval between the instant to which electrical actuation voltage is applied to the actuation device in light of obtaining a determined focal length and the instant at which the preferred focal length effectively is achieved.
This response time is connected to the capacity of the fluid to escape from the flow region towards the central part of the device or vice versa.
To boost performance of the device, generally the aim is to reduce this response time.
Document FR 2 965 068 describes a particular arrangement of the optical device for reducing the response time. In the cavity defined by the membrane and the support, this arrangement comprises a structure delimiting a main chamber at the level of the central part of the membrane and a peripheral chamber at the level of the flow region. Said chambers are in fluidic communication at the level of said structure. The geometry of the device is adapted to force the flow of the fluid through said structure of the main chamber towards the peripheral chamber or vice versa and limit the amount of fluid in the device.
But there is a need to further improve the response time of this type of optical device.